The present invention relates to strengthening the end portions of prestressed concrete members which contain strands extending through the length of the concrete member. The present invention also relates to a method and apparatus for splicing together two or more prestressed concrete members.
Splicing mechanisms are known in the prior art. For example, the Silvander, U.S. Pat. No. 4,196,557, teaches a splicing apparatus in which metallic plates are attached to the ends of concrete members. However, the plates in this device are threaded onto reinforcing rods which extend into the concrete pile. The present invention, in contrast, relates to prestressed concrete members having strands extending therethrough as opposed to reinforcing rods. The strands are relatively more difficult to work with than the reinforcing rods.
Another example of pile splices is the Grazel U.S. Pat. No. 3,545,214 which again relates to piles having reinforcing rods rather than strands extending therethrough.
The Burtelson U.S. Pat. No. 3,762,027 relates to a method of post-tensioning prestressed concrete in which tapered anchors are used in conjunction with strands. The Burtelson method is limited to post-tensioning and utilizes rather expensive sleeve mechanisms to cover the length of the strand extending through the concrete member. The present invention does not require post-tensioning of the entire strand or the use of sleeves. Other less pertinent splicing mechanisms are shown in U.S. Pat. Nos. 4,009,550; 3,988,899; 3,650,553. Less pertinent anchoring devices are shown in U.S. Pat. Nos. 3,820,832; 3,399,434; 3,895,879; and 3,912,406.
U.S. Pat. No. 3,579,931 discloses a method for post-tensioning tendons which requires a rather complex method of bending the ends of said tendons.
The Yegge U.S. Pat. No. 3,597,830 discloses method and apparatus for post-tensioning tendons in which a pair of jacks are utilized. As pointed out above, post-tensioning either requires the use of sheathing material around the strand or substantially over-stressing the strand beyond the working stress to overcome frictional effects, either of which rather substantially increases the cost of the finished member.
U.S. Pat. No. 3,029,490 teaches the use of headed wires or other fairly complex positive end anchorage to avoid the use of sheathing in post-tensioning. The present invention utilizes much simpler connectors at the ends of the strands and does not require post-tensioning the entire strand.
U.S. Pat. No. 3,163,904 teaches a strand chuck used to grip tendons in prestressed concrete members. This patent does not teach a splicing mechanism or a method for pretensioning the end portion of the strands.